IDC says in 2013, "worldwide desktop PC shipments are expected to drop by 4.3 percent and portable PCs to maintain a flat growth of 0.9 percent. The tablet market, on the other hand, is expected to reach a new high of 190 million shipment units with year-on-year growth of 48.7 percent."

So, if this was a horserace, tablets would be surging past slowing desktops and gaining on steady laptops.

Now, this is worldwide data. North American data is ahead of the game. PC Magazine reported in November 2012, "Buoyed by Black Friday sales, more tablets than laptops are projected to ship in the North American market for the first time ever in the fourth quarter — and it won't even be close, according to NPD DisplaySearch."

Fast Company said in January 2013, "This is the year tablets will occupy over 50 percent of the market, as shipments of the slate-like computers leap 64 percent over last year's figures. That stat has one important implication — that tablets will outsell laptops. In fact, NPD predicts that the trend will continue so that by 2017 laptops serve just over a quarter of the market."

Something similar to the tablet surpassing desktops happened worldwide back in February 2011, according to an AP story: "For the first time ever, smart phones such as Apple Inc.'s iPhone are outselling personal computers, according to a report by research group IDC that was released Monday. Worldwide, consumer electronics makers shipped 100.9 million smart phones in the last three months of 2010, an 87 percent jump from a year earlier. PC shipments were weaker than expected, edging up just 3 percent to 92.1 million."

Contrast this with IDC's current prediction that in 2013 "the smartphone market is expected to grow 27.2 percent to 918.5 million units."

Of course, smartphones, tablets, laptops and desktops all have slightly different uses and purposes. This data doesn't measure when people stop using desktops or laptops — but it also doesn't say how many people still use eight track tapes, either.